Method for adjusting a vehicle-mounted radar sensor

ABSTRACT

In a method for adjusting a vehicle-mounted radar sensor having three radar lobes, which are emitted in a fan-shaped manner, one of which is a central lobe, and the other two are lateral lobes extending at the same angle, a reflector plate disposed at a distance from the vehicle and perpendicular to the vehicle longitudinal axis is pivoted about a vertical axis. The deviation of the reflector&#39;s position angle from an ideal position is determined. The ideal position is one in which the two lateral radar lobes produce at least a substantially identical reflection signal. The radar sensor is subsequently pivoted by a correction angle, which is equal to the deviation of the reflector plate&#39;s position angle, but in the opposite direction.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a method for adjusting a radar sensor mountedon a motor vehicle having three radar beams emitted in a fan-shapedmanner, one of which extends centrally and the other two extendlaterally at the same angle.

The use of this type of radar sensor is expanding. The sensors areimplemented in the field of ACC (Automatic Cruise Control) devices forascertaining the distance of the vehicle from the respective precedingvehicle, and maintaining a constant distance by controlling the driveunits appropriately. A presupposition for proper function is an exactadjustment of the radar sensor relative to the longitudinal axis of thevehicle. This adjustment must be made prior to the initial systemstartup, that is, during the manufacture of the vehicle or in theassembly phase. The problem associated with this condition is that apossible misalignment by a few degrees is not externally perceptible,but can have a considerable impact on the functioning capability of theoverall system. If a misalignment has occurred, the system perceivesvehicles traveling offset ahead as being located immediately in front ofthe vehicle, while interpreting vehicles located immediately in front ofthe vehicle as traveling offset ahead.

The prior art is affected by the following problems:

(1) The reflector plate must be oriented perpendicular to the vehicleaxis, both in the vertical and horizontal directions. The use of acommon reference plane for the vehicle and reflector can assure thevertical orientation.

(2) If the reflector is oriented perpendicular to the vehicle axis, thesignals received in all of the radar channels (e.g., the left, centerand right lobes) are compared to one another. If the reception amplitudeof the right lobe is stronger than that of the left lobe, for example,it can be safely assumed that the sensor has become misaligned to theleft; the extent of the misalignment angle cannot be determined,however. The prior art is therefore a process of “trial and error.”After the direction of the misalignment has been determined, the mountedposition of the sensor can be corrected by an arbitrary angulardistance, and the measurement is repeated, until the operational sign ofthe misalignment angle changes. This iterative process is extremelytime-consuming, and is hardly suited for mass production.

It is the object of the invention to provide a method of theabove-mentioned type, which permits a simple, exact adjustment of theradar sensor.

The invention accomplishes this object by providing a method foradjusting a radar sensor mounted on a motor vehicle comprising threeradar beams emitted in a fan-shaped manner, one of which extendscentrally and the other two extend laterally at the same angle. Areflector plate mounted at a distance from the motor vehicle andvertically in relation to the longitudinal axis of the vehicle isrotated around a vertical axis. The deviation of the angular position ofthe reflector plate from an ideal position is determined, in whichposition both lateral radar beams supply an at least approximately equalreflection signal. The radar sensor is then rotated at a correctingangle that is inversely equal to the angular position deviation of thereflector plate.

The invention is based on the following concepts:

(1) The horizontal orientation of the reflector through the measurementof the distances between the rear wheels and the reflector, and the useof this information to calculate the vehicle's skew angle relative tothe reflector.

(2) The use of a reflector that can pivot by arbitrary angular distancesabout a horizontal and a vertical axis. The mounted position of thesensor must be corrected after the final vertical and horizontalmisalignment angles have been determined. Additionally, the evaluationunit for the radar signals and the adjusting mechanism of the reflectorplate are coupled to one another, which allows for a fully-automatedprocedure that requires no manual intervention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a-1 c illustrate, by way of example, the method according to theinvention.

REFLECTOR ORIENTATION

The reflector 10 is not initially oriented relative to the vehicletravel axis; in other words, the reflector 10 and the vehicle travelaxis deviate from a perpendicular position by the so-called vehicle skewangle. This angle can be calculated through the measurement of thedistance of the rear axle from the reflector (vehicle skew angle=arcsin(d1-d2/1). The zero position of the reflector is corrected by pivotingthe reflector by the angular distance of the vehicle skew angle, so thatthe reflector and the vehicle form a right angle. Thus, the vehicle skewangle equals zero.

Horizontal Adjustment

In FIG. 1a, the ACC sensor is shown with a misalignment to the left withrespect to the vehicle travel axis. For a triple-lobe radar sensor, thismeans that the signal received in the right channel is stronger than theone received in the left channel. An automatic pivoting device thereforerotates the reflector counterclockwise until the reception intensitiesin the left and right channels are identical. The reflector setting atthis time (FIG. 1b) corresponds to the difference between the originalvehicle skew angle prior to the “reflector orientation” step and thehorizontal misalignment angle of the ACC sensor. If, as described, thevehicle skew angle equals zero, the pivot angle of the reflector isequal in distance to the horizontal misalignment angle. The latter couldbe determined without necessitating a change in the mounted position ofthe sensor.

This fact, which is described in FIG. 1b, allows for an automatic sensoradjustment that can be implemented in mass production. For this purpose,the horizontal misalignment angle of the sensor is set at zero. Thesignal received in the right channel is identical to the signal receivedin the left channel.

The pivoting reflector used in accordance with the invention also offersalternative adjustment strategies, such as recording the entire antennapattern through a pivoting movement of the reflector across the entirehorizontal angular region. The misalignment angle can thus beascertained through an analysis of the measured data.

Vertical Adjustment

Because the ACC sensor illustrated in the example (FIG. 1c) does notpermit an angular resolution in the vertical direction, the followingprocedure is performed to correct an additional vertical misalignment ofthe sensor.

The reflector is additionally pivoted across the entire vertical angularregion. In the process, the signals received by all three antenna lobes,or only by individual lobes, are recorded. A subsequent analysis ofthese measured data yields the vertical misalignment angle. In this caseas well, it is not necessary to correct the mounted position of thesensor during the determination of the misalignment angle.

The mounted position of the ACC sensor is not corrected until thehorizontal and vertical misalignment angles have been determined with anautomated method. In contrast to the iterative method employed to thispoint, a single correction step suffices in the case of a horizontal anda vertical misalignment.

Hence, it is possible to make an optimum adjustment to the radar sensorquickly and simply.

What is claimed is:
 1. A method for adjusting a radar sensor mounted ona motor vehicle, the radar sensor having three radar lobes emitted in afan-shaped manner, one lobe extending centrally and the other two lobesextending laterally at the same angle, the method comprising the actsof: pivoting about a vertical axis a reflector plate disposed at adistance from the motor vehicle and perpendicular to a vehiclelongitudinal axis; determining a deviation of a position angle of thereflector plate from an ideal position angle, the ideal position anglebeing one in which the two laterally extending lobes produce anapproximately equal reflection signal; subsequently pivoting the radarsensor by a correction angle, which correction angle is equal to thedeviation of the position angle of the reflector plate but in anopposite direction.
 2. The method according to claim 1, furthercomprising the acts of: pivoting the reflector plate about an axisextending horizontally as well as transversely to the vehiclelongitudinal axis; and deriving a vertical mounted position of the radarsensor from the behavior of the reflection signals of the radar lobeswhen the reflector plate is pivoted upward and downward by a few angulardegrees relative to a position that is perpendicular relative to thevehicle longitudinal axis.
 3. The method according to claim 1, whereinthe act of disposing the reflector plate at a position relative to thevehicle longitudinal axis is performed as a preparatory step.
 4. Themethod according to claim 2, wherein the act of disposing the reflectorplate at a position relative to the vehicle longitudinal axis isperformed as a preparatory step.
 5. The method according to claim 3,wherein the act of positioning the reflector plate further comprises theact of determining distances between the reflector plate and center axesof rear vehicle wheels of the motor vehicle.
 6. The method according toclaim 4, wherein the act of positioning the reflector plate furthercomprises the act of determining distances between the reflector plateand center axes of rear vehicle wheels of the motor vehicle.